Known fertilization techniques exhibit many disadvantages. One such technique, the dry-spreader method, used primarily for lawns, uses a mechanical-cyclone or drop-spreader apparatus to spread a dry granular fertilizer. At least five kinds of waste are inherent in this method. First, while the amount of active nutrients available to plants from granular fertilizer can vary widely from brand to brand, typically a bag of pre-blended granular fertilizer might contain as much as 98% inert matter such as fillers, carriers, and coatings that merely transport a relatively small amount of active ingredients to the plants. The inert matter has no other benefit for the plants. Second, significant amounts of the active ingredients (typically nutrients) are often lost as a result of atmospheric conditions such as heavy rain or high winds and clipping removal. Third, the dry-spreader method is frequently subject to a considerable amount of un-dissolved or un-converted nutrients that have been locked up in the soil, unable to be absorbed by root system, because of an imbalance in excess of another nutrient. Fourth, since the mechanical broadcast type spreaders equipment typically cannot be better controlled, it frequently wastes a considerable amount of the granular fertilizer being applied, on to surfaces such as walkways, driveways, parking lots and patios, etc., instead of within the sub-surface of the turf and around the base of shrubs and trees beds where it belongs Fifth, attempts to achieve a “quick greening” with a dry-spreader method require excessive watering in order to begin a dissolving process of the fertilizer, so that nutrients can be absorbed into the root system more rapidly, but this over-watering can actually result in the loss of the necessary nutrients desired to produce a quick greening effect, by causing the nutrients to leach well beyond the root system. Additionally, depending upon the soil composition, such as dense clay-based soils, excessive watering may also increase the potential of nitrate (nutrient) run-off, which then also contaminates ground-water supplies, pollutes ponds, streams, and natural waterways. The loss of nitrogen through leaching, run off, and volatilization (evaporation into the atmosphere) is also a growing ecological concern.
Another critical disadvantage to using this dry-spreader applied method is early morning applications, when dew is present on the lawn, is potentially injurious to the plant, because unless the particles are immediately “watered in,” the granular inorganic particles that stick to the damp grass blades significantly increase the probability for “fertilizer burn.” On a lawn, fertilizer burn typically results in brown spots or leaf shoots turning brown (dehydrated) from the tip down. Another significant problem with the dry-spreader method is that, because the fertilizer is typically put down in rows over a lawn, frequent row-skipping or overlapping results in under or over-fertilizing, causing a blotchy or stripped appearance. When fertilizers are being applied to shrub and tree beds, the application is commonly done by broadcasting hand fulls of the product from a pail over the area. This antiquated and applicator health risk method falls short in being able to apply the products evenly throughout the shrub and tree beds. This method wastes a considerable amount of the product, since the uptake (absorption) of the essential nutrients for the plants overall benefit are locked up on the surface of bed and unable to be homogeneously absorbed by the root system of the plants.
Maintaining a balance of nutrients in the soil is an important management objective. By judicious use of fertilizers, nutrients which are deficient in soil can be supplied to growing plants. The objective of fertilizer programs is to supplement the capacity of soils as precise as possible to supply nutrients that would otherwise be deficient for normal and healthy growth.
Furthermore, to be effective, it is recommended that fertilizers that are applied by the dry-spreader method be “watered in.” That is, the particles should be in a dissolving process for the active nutrients to be eventually absorbed by the plants' root system.
It is well known that nitrogen sources that readily dissolve in water pass into solution at a faster rate than the plant, or often the soil itself can absorb them. This is a common occurrence with most powders, liquids, and some granular products that have a sulfur coating on the particles, such as sulfur-coated urea. Heavy rains or daily sprinklings will dissolve the coating of the particle too quickly, releasing too great a quantity at one time of the active nitrogen source, thus increasing a high probability of burn and stress damage to the plant, including the waste or significant reduction of the product's life span.
Another commonly known fertilization technique, the aqueous-dispersion method, uses a spray nozzle to disperse fine powders in an aqueous medium. The aqueous medium containing these fine powders is typically obtained by blending, along with other liquid fertilizers, in a tank of water, which acts as a carrier for the nutrients. The aqueous-dispersion method is typically carried out with conventional spraying equipment or by pressure injection through an irrigation system.
This aqueous-dispersion method allow formulations that provide nitrogen, phosphorous, and potassium nutrients in a liquid flowable form with an analysis usually pre-blended from the manufacturer. In order to keep these materials well blended on the spraying rig, the agitation depends upon a small propeller type fan mounted on the inside of the spraying tank.
These soluble fertilizer forms usually provide nutrients, which are immediately available to the plant, and therefore, enable quick response or “quick greening” of the lawn. But such a liquid or blended-powder solution is often too rich in immediately available nutrients and is particularly high in salt-rated nitrogen. They are mixed sparingly because of their potential for burning, and require careful monitoring of the amount of product being applied, and the number of applications required to maintain a desired appearance. They may improve some (short-lived) plant characteristics, such as shoot growth and color, but do not promote or stimulate the desired balanced root development for the overall health of the plant. Applying these rich nutrients would be an occasional “nice treat” for the plants, but not a good diet to maintain the overall health and root development, which is the foundation and life support of the plant.
Furthermore, all fertilizers contain salt. These salts are not unlike table salt except that they contain various nutrients. When a salt is added to water, the osmotic pressure of the solution is increased. Osmotic pressure, in a sense, is a measure of the force that a dissolved substance exerts on a semi-permeable membrane, such as turf grass. When a fertilizer, either as a liquid or a powder, is applied to the surface of the soil, the fertilizer salts must sooner or later enter and become a part of the soil solution before the nutrients can enter the roots and be used by the plant.
The increase in the osmotic pressure may determine whether the plant will survive or die from a fertilizer burn. Water can pass through the root cell membranes of the plant only when the osmotic pressure of the soil solution is lower than that of the solution inside the cell. If the osmotic pressure of the soil solution becomes greater than that of the solution inside the plant cell, water cannot enter the cell and may even be drawn or pulled out of it. A higher pressure pulls a lower pressure. When water and the nutrients of the soil solution cannot enter the root cell membranes of the plant, eventually this will results in the death of the cells. When the root cells die, the whole plant may die. Normally water moves from soil into a plant root, but water can move out of a root if too much fertilizer makes the concentration of salts in the soil too high. In fertilizer burn, water is drawn out of the plant as a result of osmotic pressure from the root to the soil, thereby dehydrating and killing the plant.
Liquid or powdered fertilizer solutions are characterized as being too rich in immediate available nutrients and are particularly high in salt rated nitrogen. A solution, which is too high in salt, will cause the death of the cells, which is typical of the “burning” appearance of the lawn or plant leaf caused by this high salt solution.
Some of the disadvantages associated with known fertilization methods are addressed by the slurry spray technique described in U.S. Pat. No. 4,238,072. This process consists of mixing into a large tank of water separate, raw, required plant nutrients as one large batch of nitrogen, phosphorous, potassium and other micronutrients in a dry granular form. Through agitation the granular particles are maintained in suspension within the tank, attaining a uniform distribution of the combination of soluble nutrients and insoluble nutrients. The mixture is then applied to the plants as a slurry spray. When the mixture soaks into the ground it carries with it a combination of soluble and insoluble nutrients for immediate nourishment to the plant as compared to the other methods. The majority of the insoluble granular nutrients that stay intact penetrate the sub-surface, remain there, releasing their nutrients slowly over a longer period of time.
But there are still disadvantages with this slurry spray method. Typically a lawn-care service, using the slurry spray technique as described above, will mix one large batch of fertilizer at the beginning of the day. Because of the apparatus design, as the fertilizer mixture continuously flows through its recycling pump and is returned back to the mixing tank, in addition with the mixture being exposed to continuous rising heat of the ambient temperature, the granular insoluble based products break down. This gradually accelerates the granules' soluble potency, which increases the probability of fertilizer burn, and also decreases the particle size, rapidly decreasing the granules' insoluble residual life. One can try to address this problem by adding more granule-based insoluble product at mid-day, but this will cause an imbalance in the percentage of basic essential nutrients of nitrate, potassium and phosphorous of the original batch, and further contribute to the reduced uptake of other essential nutrients. Nutrient balance is extremely important in plant nutrition. An excess of one nutrient can cause reduced uptake of another. An excess of potassium, for example may compete with magnesium uptake by plants. A heavy application of phosphorous may induce a zinc deficiency in soil that is marginal or low in zinc. Excess iron may induce a manganese deficiency.
In addition, different lawns and their conditions may require different amounts of care, and thus different fertilizer formulations. But with known methods and devices, including the slurry spray method, it is difficult to customize formulations for each job site that a lawn-care service may address on a given day. Again, the typical practice is to mix one large batch of a single fertilizer formulation at the beginning of the day and apply the same formulation regardless of the different nutrients that are required for each lawn or plant.
It would be advantageous to have methods and devices that address the disadvantages inherent in the slurry spray method along with the disadvantages associated with other methods of dry-applied mechanical spreader and liquid/powder, aqueous spray applied techniques as outlined above.